FIELD OF THE INVENTION
The present invention relates to an ink jet printing method and an apparatus for practicing said method. More particularly, the present invention is intended to reduce an occurrence that a printed image is recognized on the rear surface of a printing medium when printing operation is performed for both surfaces of the printing medium.
Conventionally, from the viewpoint of saving of paper resources, it is desired that both surfaces of a printing medium are printed. Also with respect to the ink jet printing apparatus, there is a tendency that both surfaces of the printing medium are increasingly printed with ink. Since liquid ink is used for the ink jet printing apparatus, there arises a problem that the printed image is undesirably recognized on the rear surface of a printing paper depending on the kind of the printing paper. In view of the foregoing problem, the conventional ink jet printing apparatus performs each printing operation with a low density printing mode which assures that the printed image is not recognized on the rear surface of the printing paper.
One example of the structure of the conventional ink jet printing apparatus is schematically shown in FIG. 5. In detail, a plurality of printing papers 102 received in a paper cassette 101 are successively delivered one by one to an opposing pair of conveying rollers 106 through paper guides 104 and 105 by rotating a paper feeding roller 103. Subsequently, each printing paper 102 is conveyed onto a platen 10 by the conveying rollers 106. A carriage 110 is engaged with the carriage driving shaft 108. The carriage 110 can reciprocably move in the direction of a width of the printing paper 102 along a guide rail 109 extending in parallel to a carriage driving shaft 108. The carriage driving shaft 108 having a feeding screw mechanism used therefor is rotated, accordingly the carriage 110 is driven for the purpose of scanning. To eject ink to a printing paper 102 on the platen 107, an ink jet head 111 is attached to the carriage 110.
It is also possible that a toothed belt is used in place of the feeding screw mechanism for driving the carriage 110.
The printing paper 102 of which one surface is printed by the ink jet head 111 is conducted to a change-over flapper 113 by a pair of paper discharging rollers 112. Here, in the case that a both surface printing mode is selected, the printing paper 102 is delivered into a reversible pocket portion 116 via a reversible conveying passage 114 by an opposing pair of reversible rollers 115. When a guide flapper 117 is turned to the shown position identified by a dotted line and the reversible rollers 115 are rotated in the reverse direction, the printing paper 102 is delivered to a reconveying passage 118 from the reversible pocket portion 116. Further, the printing paper 102 is fed onto the platen 107 by the conveying rollers 106. A printing operation is performed by the ink jet head 111 to the surface of the printing paper 102 located opposite to the surface which is previously printed with ink. Thereafter, the printing paper 102 of which both surfaces are already printed is conducted to the change-over flapper 113 turned to the shown position identified by a dotted line in the same manner as the printing paper 102 of which one surface is printed while the one surface printing mode is selected. Then, the printing paper 102 is conveyed to a paper discharging tray 120 via a paper discharging passage 119 by the paper discharging rollers 112.
A process of printing operations as mentioned above is shown in FIG. 6. In detail, when a power source switch (not shown) is shifted to ON side, a high quality printing mode (hereinafter referred to as HQ mode) and a one surface printing mode with which only one surface of the printing paper 13 is printed are automatically set. It should be noted that the HQ mode represents a mode with which the ink density is not lowered, that is, a mode with which an ink ejection quantity is set to an original ink ejection quantity corresponding to image information but a printing speed is not increased to a high speed.
Determination is made at a step S1 as to whether a both surface printing mode is selected or not. In the case that determination is made at the step S1 such that the both surface printing mode is not selected, the program goes to a step S2 at which ink density is lowered, that is, the present ink ejection quantity is reduced less than an original ink ejection quantity corresponding to image information. In addition, determination is made whether a high speed printing mode for increasing the printing speed to a higher one (hereinafter referred to as HS mode) is selected or not. In the case that determination is made at the step S2 such that the HS mode is not selected, the program goes to a step S3 at which one surface printing operation is performed for the printing paper 102 with the HQ mode.
On the other and, in the case that determination is made at the step S1 such that the both surface printing mode is selected, the program goes to a step S4 at which the both surface printing mode is set for the ink jet printing apparatus. Then, determination is made at a step S5 as to whether the HS mode is selected or not. In the case that determination is made at the step S5 such that the HS mode is selected, the program goes to a step S6 at which both surface printing operation is performed for the printing paper 102 with the HS mode having few occurrences that printed image is recognized on the rear surface of the printing paper 102.
In the case that determination is made at the step S2 such that the HS mode is selected, the program goes to the step S6 at which one surface printing operation is performed for the printing paper 102 with the HS mode having few occurrences that printed image is recognized on the rear surface of the printing paper. In addition, in the case that determination is made at the step S5 such that the HS mode is not selected, the program goes to the step S3 at which both surface printing operation is performed for the printing paper 102 with the HQ mode which takes preference of printing quality over prevention of an occurrence that printed image is recognized on the rear surface of the printing paper 102.
In the conventional ink jet printing apparatus shown in FIG. 5 and FIG. 6, in the case that both surface printing operation is performed for the printing paper 102, it is necessary that printing operation is performed with the HS mode in order to suppress an occurrence that printed image is recognized on the rear surface of the printing paper 102. However, when printing operation is performed with the HS mode, there arises a problem that sharpness of the printed image becomes insufficient as printing density is lowered, and consequently, excellent printing quality can not be obtained. Accordingly, in case that the printing density is set to a usual high density in order to maintain the sharpness of printed image, there intensely appears a phenomenon that the printed image is recognized on the rear surface of the printing paper. At any rate, the conventional ink jet printing apparatus has a difficulty that excellent printing quality is hardly assured.